Budget computation V/s Budget checking in purchasing

what is the difference between Budget computation and Budget checking in PO entry? I got below from knowledge garden. I'm confused as at what time the PO will go on hold, is it when budget is computed or when budget is checked based on processing option of the P4310? We are using JDE E1 9.1.

Budget Computation at PO Entry

When an account number is entered on the purchase order detail line and budget checking is activated in the processing options, the system will calculate available budget by subtracting actual and committed amounts from the available budget allocated to the account. The computation performed is: