I always seal my grout on jobs. It just makes the job completed and finished.
I find that sealed grout is best in kitchens and baths. You must seal grout three days after the grout was applied. Sealing old or dirty grout is a waste of time.
Only seal new grout.
sealing grout is a very easy task, but it does have to be re done frequently if traffic is demanding.
Only apply sealant to grout and not on the tile itself. You can test the sealant to see if it took. Usually on new grout, I go over every area three times between drying. It does dry fast.
To test the grout, fill a teaspoon or eye dropper with water. Apply a drop on the newly dried sealed area. the water should bead up like water on a freshly waxed car hood. If it does not, apply more sealant.
I like the silicon sealant that has the old fashion shoe application sponge, it makes it easy. If you do not have this, just buy a cheap foam small brush and direct the stuff on the grout area.
To test your sealant periodically do the water test. Remember, do not seal in dirt and grime, make it clean when re doing.