i have to say it - walkons add value. a lot of it. they give an extra scholarship worth of resources over a mediocre player, or any other player for that matter.
couple things to add - topdogg walking back the poorly worded recommendation to go 'all-in on one player and be fine taking 3 walkons if you miss' is a good thing. you shouldn't be THAT extreme in your approach - especially new to d1 with c+ prestige. its a fine move for an experienced coach, but like shoe said, even then you won't be all in on that 1 player 95% of the time. for a new-to-d1 coach its generally a good recipe for two things - taking 3 walkons and getting frustrated. its OK to try it, but i would recommend a new coach with zone to shoot for at least 10 players, so they have some room to miss.'
topdogg being unwilling to stand up for his idea and assert directly that walk ons have value - not so good :) 3k + 20ap for potentially 4 seasons, that is a lot of value. the overall concept is right; walkons are worth a lot and zone teams can afford to carry multiple of them. there is a lot of nuance in how many walkons one should take; most have too many or too few, few hit the nail right on the head. its also very circumstance-dependent.
that said, the concept is simple. the last player you sign, your 12 man, has to bring substantial value to your team - more than a walkon is worth - to be worth signing. signing a guy to be career backup or a 'good reserve', as i've heard people call them, is generally a pretty bad idea. your player doesn't have to do a damn thing right away, but if hes not a highly valuable starter (or perhaps a very high scoring bench player) by the end of his career - a walkon is worth more.
its the exact same concept for your 11th man or your 10th man, but its just a lot less likely you'll fill your 10th spot with a guy who brings little value than your 12th man spot. still, it happens, i see people do it all the time - sign a guy just to fill a spot, when they really don't need to fill said spot. the key to remember, its far better to have a 'useless' walkon for 1 season, than to sign a guy who hurts you by eating a spot (and the 3k+20ap that comes with it) for 4 years. even if its like, your 8th man in zone you are trying to fill, or 9th with an un-even rotation - sure, that empty spot will hurt you a bit this season, but far less than having dead weight for 4 seasons will.
i do think shoe is right people tend to under-sell the value of projects in the zone. you only need 8 'real' players, so that not only gives you room for walkons, but projects, ineligibles, etc - just like he said. but again, the most common mistake i see people make running zone is settling for mediocre players in that 11th and 12th man spot, which is really awful if you are running zone. take the walkons. its OK in press, but a disaster in zone.