Full Idea
One possibility is that talk of sense-data is a mere linguistic convenience, providing a noun for talking about appearances, as when seeing a red object in sodium light (when it looks grey).
Gist of Idea
Maybe 'sense-data' just help us to talk about unusual perceptual situations
Source
A.R. Lacey (A Dictionary of Philosophy [1976], p.196)
Book Reference
Lacey,A.R.: 'A Dictionary of Philosophy' [RKP 1976], p.196
A Reaction
The term seems to have been coined to deal with situations where there is a gap between appearance and presumed reality, as in illusions. Maybe illusions prove the existence of sense-data, rather than it being a 'convenient' term.