ORJ, as above from decurion, reverse is very effective on wet / slippery runways (N.B. ‘slippery’ is a Boeing term which includes wet / very wet).
See
ALAR Briefing Notes in English | Flight Safety Foundation , chapts 8.4 & 8.5, where diagrams show the components of braking.
Although reverse is not included in EASA dry / wet landing performance, incident statistics suggest that many pilots rely on reverse to rescue unforeseen / poorly judged situations, thus its use is recommended by internal SOP.
Note that when using EASA contaminated landing performance, reverse thrust may be assumed, if so then it must be used. The performance data should be annotated as such and details provided of limiting circumstances and/or assumptions (CS AMC 25.1591).
EASA - Certification specifications
The reference to 140% is unusual. Either the operator follows FAA type rules with airborne assessments calculated as suggested in posts above, or if an EASA operation, a particular interpretation of EU-OPS 1.400 is used. I.e. a requirement for safe approach and landing – if a 1.92 factor is required for dispatch how is 1.4 factor in the air, justified as being ‘safe’?