we had such practice in one of my past applications.
What we were doing was closing BOP while WOC and connecting cementing pump unit to annulus to keep some extra pressure in it.
The reason for that was a phenomenon when hydrostatic pressure in annulus while WOC is equal to water pressure (something around 1sg) because cement slurry is getting harder and hard structure is built whereas among the hard cement clusters we still have "free water". The water cannot withhold our pore pressure and gas/oil/water (whatever you have in the reservoir) starts moving up from the formation toward to surface, creating kind of worm holes (channels)which worsening your cement isolating properties and you may see it on your CBL.
Hope it will help.