For good growth of roots and the plant a good equal of air and water is ideally maintained in the soil.

All plants have a preference for the amount of water they like in the soil. Begonia and Fuchsia like it on the wetter side.

Where African Marigolds Tagetes erecta and Rudbeckia like it on the dryer side.

For sturdy/strong growth, Chrysanthemum are grown on a wet/dry growing regime.

If constantly wet growth will be lusher and possibly more susceptible to diseases, to the point where if water-logged roots may be killed.
If constantly kept too dry, plants will be stressed and will not grow well. If allowed to wilt leaves may be scorched and flower buds may drop (Fuchsias).