Shaykh Saalih Al Fawzaan was asked about those who follow the legislated Islamic concessions?

The religion is an amaanah- an amaanah between the slave and his Lord. It’s obligatory that he performs it (the religious duties) as Allah and his messenger have commanded. Whoever performs the obligations, leaves off the prohibited affairs, (does) that which he is able from the mustahabbaat (recommended actions) and abandons the makroohaat (disliked affairs), this is the amaanah between the slave and his lord.

The concessions are only allowed when there is a need and necessity (to utilize) them. Utilize them in accordance with necessity- with a need for the concession. Just like the sick person combines between two prayers, performs tayyamum if he cannot use water for purification and doesn’t fast in Ramadhaan, and a traveller shortens the prayers- this is a religious concession used at the time of its requirement.

As for using concessions in other than their correct place,(i.e. situation) then this is not permissible. Allah did not permit that for him (in such situation). Indeed He (Allaah) only placed the concessions at specified times and situations, and they are not used in other than these (times and situations).  Therefore it is obligated on the Muslim that he fears Allah and that he establishes that which Allah has obligated on him. [Abridged]

http://www.alfawzan.af.org.sa/node/13751