The fact that mainstream ‘high street’ adult shops find it worthwhile to also stock some bondage equipment suggests that some otherwise ‘vanilla’ couples incorporate elements of bondage into their sex lives at some point in their relationships. Leaving aside those couples who are themselves part of the BDSM ‘community’, the use of bondage within couples tends to be very different to and separate from that normally associated with BDSM. Couples’ private bondage games largely take place behind closed doors, and constitute foreplay, usually as a prelude to the couple having sex. There may or may not be some elements of dominance and submission involved as part of role play, but sadism and/or masochism rarely play any part unless the couple already have such leanings. This contrasts with activity in the BDSM subculture, where the emphasis is often more on bondage for its own sake, frequently ending in masturbation only, or indeed involving no sexual contact at all. These differences can lead to misunderstanding if couples who have tried private bondage games encounter the BDSM subculture. Trusting couples can't understand the need for safe-words, while the members of the subculture can't understand why couples mainly see bondage as a part of sexual intercourse.
Bondage within couples usually involves one partner being voluntarily tied-up or put into restraints (i.e. bound / cuffed / spread-eagled etc) by the other, who then either sexually pleasures the tied partner (using manual masturbation, oral sex, vibrating sex toys etc.); or has sex with them while they are restrained, or of course both. The erotic appeal is often in the form of feedback from the writhing / struggles / vocalizations etc of the tied partner. The tied partner may derive pleasure from being in a largely ‘helpless’ predicament in the hands of a trusted partner, and the other may enjoy the mild domination involved in having their partner in that predicament. Either way, many established couples find playing bondage games relationship-affirming, as they both require and imply a level of trust between the partners that is not normally found within more casual relationships, as well as being a shared ‘private’ facet of their sex life that most couples prefer to keep just between the two of them.
This form of bondage has its own niche on some internet websites, where images and movies usually depict voluntarily-tied models undergoing inescapable intense sexual pleasuring, rather than any menace, force or pain. Safety rules followed by couples are frequently context - and trust - based. As the tied partner will more often than not be held in a submissive sex position, sex therefore takes place with their pre-agreed consent. For example a still photograph taken out-of-context at that moment would suggest a very different story to that of a consensual sex game / mutual rape fantasy enactment etc.
Here is another great lesdom story of two lesbian couples who loves to play with ropes I met up with Ursela and Marcy in their apartment. Hanging out on an average day, Ursela enjoys keeping Marcy tied up much of the time and takes great pride her ropework. 
