vorteilhaft
advantageous
Bringing an advantage or benefit; having a positive effect.
Regelmäßige Bewegung ist vorteilhaft für die Gesundheit.
Regular exercise is advantageous for health.

advantageous / flattering
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advantageous
Bringing an advantage or benefit; having a positive effect.
Regelmäßige Bewegung ist vorteilhaft für die Gesundheit.
Regular exercise is advantageous for health.

The adjective is derived from the noun 'der Vorteil' (advantage). The ending '-haft' turns nouns into adjectives and means something like 'having the quality of something'. 'Vorteilhaft' (advantageous) therefore literally means 'having an advantage'.
Diese Entscheidung war für alle Beteiligten vorteilhaft.
This decision was advantageous for everyone involved.
When you want to express for whom or what something has a benefit, you use the preposition 'für' followed by the accusative. This construction is very common.
Eine frühe Planung ist für den Projekterfolg vorteilhaft.
Early planning is advantageous for the success of the project.
In the context of clothing, hairstyles, or photos, 'vorteilhaft' (flattering) means that something positively highlights or flatters a person's outward appearance.
Diese Hose hat einen sehr vorteilhaften Schnitt.
These trousers have a very flattering cut.
In a business or financial context, 'vorteilhaft' (advantageous) means that something is favorable or profitable. Pay attention to words like 'Preis' (price), 'Angebot' (offer), or 'Konditionen' (terms).
Die Bank hat uns sehr vorteilhafte Konditionen für den Kredit angeboten.
The bank offered us very advantageous terms for the loan.
interesting
'interessant' and 'vorteilhaft' can both fit in situations where something brings a benefit. This is especially true for offers, contracts, or business decisions. 'interessant' often sounds a bit more general: something may be worthwhile or worth looking into more closely. 'vorteilhaft' is more precise and clearly says that something has an advantage or has a positive effect. If you only want to say that an offer deserves attention, 'interessant' fits. If the benefit is the focus, 'vorteilhaft' is clearer.

Für die Ärztin ist ein früher Termin vorteilhaft, weil sie danach noch Hausbesuche macht.
For the doctor, an early appointment is advantageous because she still makes house calls afterward.
Das neue Angebot ist für die Schule interessant, weil es Geld spart.
The new offer is attractive for the school because it saves money.