Collins was the long-established "gold standard" for amateur radio equipment. The 32S-3 quotes carrier and unwanted sideband suppression at -50dB; the later, solid-state KWM-380 improved opposite-sideband suppression to -55dB. The Signal/One CX-7 made a big splash in the amateur market; carrier and unwanted-sideband suppression are listed at -60dB. Modern rigs like the Elecraft KX-3 use less expensive modern digital and mixed-signal means to deliver 60dB or better suppression without using crystal or mechanical filters.
In the era of the 32S-3, amateurs in the US were limited to 1000W DC input power. At the roughly 50% practical efficiency of class AB amplification, the legal output limit would be around 500 watts. 50dB of suppression would have limited the opposite-sideband power to approximately 10 milliwatts! This would have been extremely unlikely to disturb adjacent stations unless they were very close to the transmitter. In the current era, 60dB of suppression means that a 1500W legal-limit signal would be reduced to 1.5 milliwatts!
INRAD still produces crystal filters for such "vintage" equipment. In addition to the IF frequency, these units are characterized by "shape factor," the ratio of the bandwidth at -60dBc to the bandwidth at -6dBc. A typical 8-pole, 2.1kHz filter exhibits a 1.5:1 shape factor:
Clearly, the attenuation continues past -60dBc, but this demonstrates the useful limit as perceived by companies' marketing departments!
For comparison, here is the shape of a 5-pole crystal filter shipped by one of today's leading amateur equipment manufacturers:
Note the much gentler "skirts" on the filter passband, resulting in a shape factor of about 3:1. "Baseband" filters, whether analog or DSP, may be used to combat interference and/or restricted emitted bandwidth.
Despite the relatively high cost compared to "phasing" gear, nearly all SSB transmitting equipment used the filter method, to take advantage of its superior opposite-sideband suppression performance. (Note: carrier suppression results from the use of balanced modulators.) It may be speculated that the "transceiver" owes its existence to the desire to control product cost and improve receiver performance by sharing the expense of the IF crystal or mechanical filter between transmitting and receiving duties. The low cost and high performance possible with modern digital and mixed-signal technologies may encourage a return to separate receiver and transmitter units to permit independent optimization of the respective signal chains.