"Since only in exceptional cases complaint can seek a compensation from the respondent "
No. Under no circumstances can a UDRP complainant obtain any kind of monetary award. The sole remedy available is transfer of the domain name.
The respondent can, of course, do nothing. However, if the respondent would prefer not to have a published opinion, then it is preferable to seek to terminate the proceeding and transfer the domain name. For example, the respondent may have a good portfolio of generic domain names - some of which might be trademarked terms for an unrelated class of goods or services (e.g. "cheer" is a common word and a trademark for detergent). In such circumstances, if the particular domain name at issue is not worth defending, then it is helpful not to have an opinion published which will be cited by others that the respondent is a cybersquatter, in cases having less merit than the present case.
The other motivator is that parties with questionably valid trademarks sometimes want to obtain a UDRP ruling, so that they can then use that as evidence that someone had recognized the validity of their mark.