Residential Flats can be legally used for office work by professionals like Doctors, Lawyers, Architects, Tuition & Yoga classes. No statutory permission is required from any Govt. authorities, since these does not imply change of residential user, which typically means change of user to commercial usage.
For self-employment, while staying in the Flat, the owner (& not tenant) can use part portion of his Flat for purposes of some business activities, that do not cause nuisance to the other flat owners. Activities like Coaching classes, Sewing, Dance, Papad making and so on are part of self-employment process.
Any other activities apart of above are normally not within the parameters of "residential activity" and falls under commercial or industrial usage.
Keep Smiling .... Hemant Agarwal