I always use a spacer under bottom row for the afore mentioned reason. It gives a better seal and movement or worktop removal doesn't mean pulling tiles back off.
As a few have already said on here i always leave a spacer gap between worktop and first row of tiles, (a 2mm spacer same as what i use on the rest of the tiles) for me it's a far neater finish (Silicon flush with tile) and the Silicon goes under the tile giving a far better seal.
As a few have already said on here i always leave a spacer gap between worktop and first row of tiles, (a 2mm spacer same as what i use on the rest of the tiles) for me it's a far neater finish (Silicon flush with tile) and the Silicon goes under the tile giving a far better seal.