@OP: As stated, a good table saw is the foundation of any decent woodworking shop. If you are doing intricate joinery with hardwoods, then sanding and making corrections is always going to be necessary, but if you are talking about joining sheet stock together, the first thing to do is tune up your tools and learn to use them properly. If you don't have the means to get a decent table saw fence, then learn how to make an accurate and straight cut with the one you have. MOST fences are not self squaring, so you need to measure both the distance from the blade to the fence on the front of the blade AND on the back. As stated, use the same measuring tool as much as you can.
A T-Square fence is one of the most valuable tools to a woodworker. I prefer Biesemeyer, but as long as it is a decent quality T-square fence, you can rely on it to make straight cuts. If you tune it up right and take care of it, it will be accurate. I haven't used my tablesaw in over 6 months, and I have dragged it around the shop, stacked stuff on it, etc, yet I could go out there right now and using only the fence to measure, get within 1/32 of an inch on a rip. If I take the time to dial it in, re-square everything from scratch, and set it all up again, I can rely on cuts accurate to 1/64th, and this is using a 35 year old Delta contractor saw base. I bought the saw used 13 years ago for $300, paid $300 for the fence, and built a table myself that turns it pretty much into a cabinet saw. I went with the 50" contractor fence and built the table to handle it. Then I built detachable feed tables so when it is all set up I can rip 4x8 sheets alone and always do them perfectly and safely. I used to build enclosures for subwoofers for car and home stereo systems. Those require air-tight seams in order to get the best results, and I built hundreds and hundreds over the years. The difference between a good tool and a crappy one (when the user is skilled) is the amount of time it takes to get a good result. If you use cheap tools you will probably spend more time setting up, making accurate cuts, and then correcting mistakes than if you had better tools.
As for buying a table saw and never using it, I disagree completely. There are a few power tools every "handyman" should own. A drill, a skilsaw, a router, and a tablesaw. Add in a few hand tools like a hammer, screwdrivers, some clamps, and a couple chisels, and you could build anything from an end table to an entire house with your tools. A table saw is the foundation of a woodworking shop. I am just a hobbyist these days and I might go a year without touching my tablesaw. But I bet over the last 13 years I have run well over 10,000 feet through that saw. Every project I do, whether it is a home renovation project, building furniture or cabinets, or just tinkering with wood in the shop ends up with me using the table saw sooner or later. Sure, you could get away without one (between a router and a skilsaw) but face it, there is no better tool to rip a 1/2" strip of hardwood off a 10' long 3/4" wide oak board. Try doing that with your skillsaw and a guide... at a 10.5 degree angle.
As for mistakes, we all make them. A good woodworker is good at covering up mistakes. When using MDF or plywood, it might be inconvenient to start over, but it won't break the bank if you make a bad cut. When using hardwoods that cost $4-$15 per board foot, you make a mistake and it is a choice between spending another $200 on materials or just making an adjustment and covering up the mistake. With hardwoods you usually can't just bondo and move on, the finished product will be stained and sealed, so sometimes it is unavoidable to just start over with mistakes. The more you learn and the more patience you have, the fewer mistakes you will make and usually they will be small enough to be able to be fixed without it affecting your project.