If you put too much sealant on concrete it will lead to bubbling, flaking and a buildup of trapped moisture in and on the concrete.
Putting too much sealer on concrete can also cause the concrete sealer to lose it's adhesion and unevenly darken the surface of the concrete.
Excessive use of sealer on concrete can trap in gas or moisture below the surface of the concrete and cause it to bubble or blister.
Applying heavy coats of concrete sealer will often not adhere to the concrete properly and can flake off the concrete over time, especially in areas where the concrete has high traffic or is in direct sunlight.
The over application of concrete sealer can also create a barrier which prevents moisture from escaping from the concrete and lead to moisture buildup and even possible damage to the concrete.
And applying too much concrete sealer can also cause uneven darkening of the concrete and create blotchy or streaky appearances, especially if you use solvent based concrete sealers.
And applying too much concrete sealer to the concrete can also interfere with the concrete sealers ability to bond properly to the concrete and lead to a shorter lifespan and reduced durability of the concrete.