I agree with the others that you build jigs when you need them.
Nobody has mentioned my problem, which is finding the time to build nice, quality jigs that I can use over and over. Instead, I build far too many one-and-done jigs of low quality, and often a higher safety risk. It is so tempting and easy to cobble something together that does the job just well enough to "get away with it."
Add to it the pressure to build real projects. You could spend a day or two building a super crosscut sled, but when the day is done, you walk out of the shop empty handed, and your family wonders what you did with all the time.
I see guys come into our woodworking club with handmade squares, jigs, and other shop gadgets. They are tools for real work, finished to last many lifetimes. I would love to have nice things like that. Sometimes I buy what I need at the local Rockler, but would prefer to make my own. Commercial sleds and jigs are available from many sources, but you can build them yourself for a tiny
fraction of the cost.
Instead of building or buying the crosscut sled that I truly need, I keep grabbing a straight board and clamping it to my miter gauge as a "miter fence". It isn't the same. What I need is a true crosscut sled, but a good one takes time to make.
I am making a simple oak wall shelf for my spouse. I needed to straighten and joint one edge of the board. Instead of a nice straight line jig like @woodnthings
made, I grabbed a straight board from the pile, put on a bunch of double tape, and jointed the edge of the oak board. It was the same the last time I jointed a board, and the time before that, ad infinitum.
It is hard to stand there and look at a board that needs an edge jointed. I could take the time to buy parts and build a straight line jig ... or in the drawer there is plenty of double tape ready to use.
The solution is obvious. I am not seeking advice for what is a time management and self-discipline issue. All I want is to share the warning with @clschaffer
A long time ago, I learned a rule-of-thumb that says, "If you repeat the same task three times, automate it."
I have heard that the definition of "idiot" is someone who repeats the same mistake over and over, but hopes for a better outcome.
Decent hold down clamps aren't cheap. I just bought some cheap ones at eBay (4 for $7.50). They are tiny; too small to be useful for a straight line jig. The photos didn't indicate how small they are, and I assumed that they were the same size as the ones woodnthings used. I was wrong. They are nearly useless toys. As usual, if the price is too good to be true...