From the late '60s, on my first ship, any drill 1/4 inch and smaller was considered expendable. It needn't be accounted for once the job was done. As an electrician, the shop had their own drill motors, no need to hang a tag for one. The point is that I have a few drills that date back to those days. And have added to my "collection" in the years following. When I started buying "sets", most of the smaller sizes had plenty of spares. It's hard to say "get this, don't bother with that." When I need a particular size, I go whole hog and get a set of that series. Some have never been used, but one never knows when. . . The one exception to this philosophy is the "jet" boring drills. 61-80. I use those on my models, and they get bent, broken, and lost very easily. I keep 3 or 4 sets as backups, new in the package. A Nr 60, the smallest in a number set, is ~1mm, 0.040 thou. It's rare when a person needs a drill smaller than 3/64.
Look at what you do, and buy appropriately. If there is lots of wood work, a cheap set of fractional and augers for larger sizes will suffice. For general mechanical work, a set of 1/16 to 1/2 fractional, of better quality than the wood bits. For machine work, a set of number and letter sizes is actually better than a fractional set. And if much metric work is done, a set of 1-13mm is handy to have on hand. For those last couple of sets, machinist and metric, you want the best you can swing. Cobalt drills are nice for harder steels, but will be overkill for general shop use. Get them when/if you can, but not as priority one.
Then there are the "esoteric" drills that are never needed until they are. Such as the size for a 3/16 pop rivet. There is no "standard" size for that. 0.1875 or 3/16 is the closest. A pop rivet hole needs to be a couple thou oversized. In the aircraft industry, there is a 0.189 inch drill specificaly for 3/16 rivets. It is of no common set, but is handy if you stumble over some in a salvage operation like I did. They were cheap, dollar a dozen cheap. And I stashed them away "just in case". Years later while working on an aluminium trailer, 3/16 rivets were needed. The 1/8 rivets had wallowed out the holes (Nr 30) and needed to be refitted with 3/16. I just happened to have on hand the right size drill. . . Or those (obsolete) "bell hanger" bits. A wood bit, 1/4 dia and 2 plus feet long. Rare but handy if you happen to have need of one.
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