There's different wattages for different floor finishes, bases and rooms.
100w/m2 mats are generally used only to give you a warm floor, these mats can be laid directly onto a timber base as they wouldn't cause it to warp. These can be used with any floor finish, however with a Wood or Carpet you'd need a 10mm Flexible SLC over the top.
160w/m2 mats are used for a primary heat source within a standard insulated room. (That's floor and wall insulation) These mats are the most popular as they offer a primary heating source without the need for any other heating source within the room. These are mainly used with tiles however can be used with Wood or Carpet restricting the floor temperature to 27 degrees.
200w/m2 mats are designed for high heat loss areas like a conservatory, these mats give off a higher output due to the cables being spaced closer onto the mesh. These mats will also heat up quicker as well due to the way they're spaced.
Generally all these mats will reach your desiered temperature however in different times but also the high wattages will maintain the heat for longer due to closer spacings on the mat. The reason the decoupling options can't be used at 200w/m2 is we only supply a 10w/m loose wire and the options on the membrane are to closely spaced for one spacing, this could cause the cables to burn out due to being to close. Our minimum distance between cables is 50mm.