I don't get why people would want the extra money in coach payroll?
I transfer a ton of money into prospects (usually I get my prospect above 30M), and I do it all from player payroll. I just think it's way more flexible. If you have a ton of extra money in coaches, the only thing that's useful for is prospect payroll. But if you stick the extra money into player payroll you have more options.
For example, say my payroll budget is set at 80M, but my "true" payroll (of guys actually signed under contract) is only 66. So I could potentially get to 27M for an IFA. That big IFA comes along that I want and I get him for 24M, which means I needed to transfer 8M from payroll to prospects. Which means I have 6M surplus left. I could use that to get another 3M into IFA, but usually that's not going to get an ML-caliber player. So I take a look at the "leftover" FAs. There's often a couple guys out there that weren't worth the 5M they were asking for initially, but have now dropped down to around 1M a piece, but everybody has already filled their roster. So you can sign them to 3-5 year deals at well below market-value and improve your bench in future seasons, especially if you front-load the contracts as much as possible.
It just doesn't really make any sense to me why people would rather have surplus coach payroll rather than surplus player payroll.
Generally speaking, I either set my coach payroll to 7M (if my fielding instructor is coming back) or 11/12M if I need to replace my FI. In time, I think most owners arrive at a pretty similar conclusion with kind of 2 or maybe 3 sort of "defaults" based on what coaches are coming back. As tec mentioned, if you have to transfer money out of coaches, you either screwed up or got outbid on an expensive coach (usually a FI) at the end and got stuck with a cheap scrub.