(a) Mary always leaves for school at 7:45
(b) Mary is always leaving her dirty socks on the floor for me to pick up! Who does she think I am? Her maid?
(c) I am always/forever/constantly picking up Mary's dirty socks!
In sentences referring to present time, usually the simple present is used with always to describe habitual or everyday activities, as in (a).
In special circumstances, a speaker may use the present progressive with always to complain, i.e., to express annoyance or anger, as in (b).*
In addition to always, the words forever and constantly are used with the present progressive to express annoyance.
*COMPARE :
"Mary is always leaving her dirty socks on the floor" expresses annoyance.
"Mary always leaves her dirty socks on the floor" is a statement of fact in which the speaker is not necessarily expressing an attitude of annoyance. Annoyance may, however, be included in the speaker's tone of voice.